Mechanism Of Interaction Of Amphiphilic Peptides With Lipid Membranes

During the past several years, Multi-drug resistence bacteria have been influencing the antibiotics activity. Amtimicrobial peptides are ancient components of the innate immune system and have been isolated from tissues and organisms ranging from prokaryotes to humans, and some of them have been used in clinic. But the technologies of isolation and purification are costly and difficult. Among the various antimicrobial peptides,α-helical cationic antimicrobial peptides possess either selectivy activity toward a certein type of cell or microorganism, or a broad spectrum of activity toward several types of cells including prokaryotic and mammalian cells. Since the 1980s, a number of models for peptide interaction with membrane have been proposed, such as"barrel stave","toroid pore"and"carpet mechanism", but the mechanisms of antimicrobial peptides action following their initial interaction with biological membranes, by which peptides may permeabilize and traverse microbial membrane are not entirely clear and likely vary for different peptides. Our team designed a series of amphiphilic peptides G(IIKK)_xI-NH₂(x=1,2,3,4) and GKI(KKII)₂KII-NH₂ according helical-wheel rule, and synthesized by solid-phase peptide synthesis (SPPS). Study peptides activity of antimicrobial was shown to have ability agsinst bacterias(Bacillus subtilis 168 and Escherichia coli 5a); Theα-helicity of these peptides was demonstrated by circular dichroism spectroscopy in the presence of DPPG (dipalmitoyl-phosphatidylglycerol, sodium salt) liposomes, and random-coil in the DPPC (dipalmitoyl phosphatidylcholine) liposomes; these peptides have cytoplasmic membrane damage activity observed by SEM(scanning electron microscope). So we study these peptides interaction with phospholipids(DPPC,DPPG, POPC [1-palmitoyl-2- oleoyl- phosphatidylcholine] and so on) monolayer membrane via LB monolayer technology that revealed the DPPG , POPC and POPG are preferred attacking components; The interfacial activity of all peptides increases with the increase of peptide chain, and GKI(KKII)₂KII-NH₂ have interfacial activity stronger than G(IIKK)₃I-NH₂; The ability of interaction between peptides and lipid monolayers declined because of lipid solution were mixed with 10%(w/w) cholesterol; Cationic Ca²⁺ and Na⁺ can effect the interaction rate of peptides with lipid monolayers; The ability of interaction between peptieds and total lipid extraction monolayer of Escherichia coli 5a was stronger than the lipid of Bacillus subtilis 168. By the above experiments, we predicted these peptides interacte with negative charged lipids and unsaturated phospholipids firstly, destroys the structure and integrity of plasma membrane, at the same time its comformation transformed also. And the regular amphiphilic structure of the peptides facilitated its penetrated into the plasma membrane, then the peptides interacte with the negative charged intracellular biological macromolecules and affects the normal physiological function of cell.